This invention relates to audio amplifiers and, more particularly, to audio amplifying systems including push-pull amplifiers with means for muting the output of these amplifiers.
Many types of muting or squelching systems are known. One such squelch system requires the receiver to be turned off unless a specific tone is accompanied with the carrier. Another type of squelch system requires the carrier to be present to permit reception of the received signal. In present two-way radio systems, it is also desirable to mute the output when transmitting. It has been found desirable to provide the muting or squelching of the receiver in the final output stages. These output stages for driving the speaker are usually push-pull amplifiers. A difficulty in muting push-pull amplifiers is that both active devices must be simultaneously biased off to prevent unwanted transients in the speaker. It is also desirable to provide some means for simultaneously turning off these push-pull driver amplifiers without using shunting devices which pass large currents when the receiver is being squelched or muted.